The present invention generally relates to rearview mirror assemblies for vehicles, and more specifically relates to rearview mirror assemblies incorporating one or more components for providing hands-free telephone use in a vehicle.
Portable handheld cellular telephones have become very popular due in large part to their portability. However, recent concerns have arisen that the use of handheld portable cellular telephones in a vehicle is a dangerous distraction that may cause accidents due to the need of the driver to hold onto the telephone and dial numbers and to also hold the telephone to the driver's ear rather than keeping both hands on the steering wheel. As a result, some governments have responded by prohibiting the use of a handheld cellular telephone while driving. Thus, the need for hands-free telephones for use in vehicles has increased significantly.
Although hands-free telephones have been previously integrated in vehicles, they have not become very popular due in large part to the need for the driver to have a separate cellular telephone service contract with the service provider associated with the vehicle-installed telephone. Although a driver could reduce the number of such service contracts by eliminating their portable handheld cellular telephone, most people have been reluctant to do so due to the fact that the vehicle-installed telephone cannot be removed from the vehicle and used elsewhere.
Commonly assigned United States Published Patent Application No. 2002-0032510 A1 discloses a system whereby a microphone and speakers may be installed in a rearview mirror assembly along with an audio and data transceiver, such as one implementing the Bluetooth™ protocol. The '510 published patent application further discloses that, when placed in a vehicle and used with a portable handheld cellular telephone that incorporates a similar audio/data transceiver, the vehicle occupant who brings such a handheld portable cellular telephone into the vehicle may utilize the microphone and speakers in the rearview mirror assembly as a hands-free telephone while still utilizing the cellular transceiver in the portable telephone and hence requiring only a single service contract with a cellular telephone service provider.
With vehicle-installed hands-free telephone systems, it is typically desirable to utilize the vehicle's existing audio system as the speakers during a telephone call. This eliminates the need and cost of providing additional speakers elsewhere in the vehicle. However, some vehicle audio systems do not include an audio input jack that would enable use of the speakers by the hands-free telephone system. Further, even in vehicles that come with a standard radio having an audio input jack, there is the possibility that the vehicle owner may replace the radio with an after-market radio that does not include such an input jack. In addition, if the hands-free telephone system is sold as an after-market system, it may be difficult to access an audio input jack on the rear of the vehicle radio and to run the appropriate wiring. Although it may be possible to utilize an audio and data wireless connection between the vehicle's radio and the hands-free telephone system, many vehicle radios are not currently equipped with audio and data wireless transceivers. For these reasons, it may be desirable to incorporate and utilize internal speakers within the rearview mirror assembly.
Providing speakers in a rearview mirror assembly presents several challenges. First, the speakers have to be relatively small and yet create an output loud enough to be clearly heard over the typical background noise present in a vehicle. Second, the hands-free microphone, if exposed to the loudspeaker output, will become overloaded. Even when switching is used to shut off either the speaker or the microphone, this overloading can cause problems. Switching, though common in hands-free telephones, is generally undesirable and can be avoided provided the speaker sound is not loud relative to the driver's speech level at the microphone. Thus, there is the need for a rearview mirror assembly that incorporates speakers for use in a hands-free telephone system and that incorporates such speakers in such a manner so as to not interfere with the sound picked up by the microphone subassembly, which is also located on the rearview mirror assembly.
It has long been desired to improve microphone performance in devices such as communication devices and voice recognition devices that operate under a variety of different ambient noise conditions. Communication devices supporting hands-free operation permit the user to communicate through a microphone of a device that is not held by the user. Because of the distance between the user and the microphone, these microphones often detect undesirable noise in addition to the user's speech. The noise is difficult to attenuate. Hands-free communication systems for vehicles are particularly challenging due to the dynamically varying ambient noise that is present. For example, bi-directional communication systems, such as two-way radios, cellular telephones, satellite telephones, and the like, are used in vehicles, such as automobiles, trains, airplanes, and boats. For a variety of reasons, it is preferable for the communication devices of these systems to operate hands-free, such that the user need not hold the device while talking, even in the presence of high ambient noise levels subject to wide dynamic fluctuations.
Bi-directional communication systems include an audio speaker and a microphone. In order to improve hands-free performance in a vehicle communication system, a microphone is typically mounted near the driver's head. For example, a microphone is commonly attached to the vehicle visor or headliner using a fastener such as a clip, adhesive, hook-and-loop fastening tape (such as VELCRO® brand fastener), or the like. The audio speaker associated with the communication system is preferably positioned remote from the microphone to assist in minimizing feedback from the audio speaker to the microphone. It is common, for example, for the audio speaker to be located in a vehicle adapter, such as a hang-up cup or a cigarette lighter plug used to provide energizing power from the vehicle electrical system to the communication device. Thus, although the communication system designer knows the position of the audio speaker in advance, the position of the microphone is unknown as the user can position the microphone where he/she chooses. The position of the microphone relative to the person speaking will determine the level of the speech signal output by the microphone and may affect the signal-to-noise ratio. The position of the microphone relative to the audio speaker will impact feedback between the speaker and microphone. Accordingly, the performance of the audio system is subject to the user's installation of the microphone. Additionally, the microphone will typically include a wire, which, if it is mounted to the surface of the vehicle interior, will not be aesthetically pleasing. Alternatively, if the wire is to be mounted behind the interior lining, the vehicle interior must be disassembled and then reattached so that the wire can be hidden, which may result in parts that rattle loudly or hang loosely from the vehicle frame.
One potential solution to avoid these difficulties is disclosed in U.S. Pat. No. 4,930,742, entitled “REARVIEW MIRROR AND ACCESSORY MOUNT FOR VEHICLES,” issued to Schofield et al. on Jun. 5, 1990, which uses a microphone in a mirror mounting support. Although locating the microphone in the mirror support provides the system designer with a microphone location that is known in advance and avoids the problems associated with mounting the microphone after the vehicle is manufactured, there are a number of disadvantages to such an arrangement. Because the mirror is positioned between the microphone and the person speaking into the microphone, a direct unobstructed path from the user to the microphone is precluded. Additionally, the location of the microphone on the windshield detrimentally impacts microphone design flexibility and overall noise performance of the microphone.
U.S. Pat. Nos. 5,940,503, 6,026,162, 5,566,224, 5,878,353, and D 402,905 disclose rearview mirror assemblies with a microphone mounted in the bezel of the mirror. None of these patents, however, disclose the use of acoustic ports facing multiple directions, nor do they disclose microphone subassemblies or systems utilizing more than one microphone transducer. The disclosed microphone subassemblies do not incorporate sufficient noise suppression components to provide output signals with relatively high signal-to-noise ratios, and do not provide a microphone having a directional sensitivity pattern or a main lobe directed forward of the housing and attenuating signals originating from the sides of the housing.
U.S. Pat. Nos. 5,732,143, 5,825,897, 4,737,976, 5,835,607, 5,754,665, 5,917,921, 5,546,458, 5,353,376, and 5,212,764 disclose various hands-free or voice recognition systems for use in vehicles. These systems employ two or more microphone transducers typically arranged in a horizontal linear array. Some of the above-noted patents disclose placing the microphones in or near the seats of the driver of the vehicle while others do not specifically disclose how the microphones are mounted in the vehicle. Some of these patents illustrate the microphones being disposed on or around the vehicle headliner in the vicinity of the front windshield. None of these patents, however, address the specific problems associated with mounting microphone subassemblies in a rearview mirror assembly.
Commonly assigned PCT Application Nos. PCT/US00/31708, PCT/US02/04359, and PCT/US02/32386 disclose various forms of microphone subassemblies integrated into a rearview mirror assembly. The various constructions of the microphone subassemblies and their positioning and integration within the rearview mirror assembly address various different problems associated with mounting microphone subassemblies on a rearview mirror assembly. Some of these constructions included a microphone subassembly mounted to the bottom of a rearview mirror assembly where the microphone subassembly included one or two microphone transducers ported to both the front and rear of the vehicle. In other constructions, a microphone subassembly was mounted on the top of the mirror and included one or two microphone transducers. An advantage to mounting the microphone subassembly on top of the rearview mirror assembly is that noise from the defroster or climate control system is not as prevalent at the top of the rearview mirror assembly. However, the microphone subassembly mounted to the top of the rearview mirror assembly is more likely to be impacted by the direct laminar airflow from the windshield defroster. Accordingly, an air deflector or other airflow defense mechanisms are built into the embodiment employing the microphone on the top of the rearview mirror assembly. In yet another of the various constructions disclosed in the above-noted PCT applications, two separate microphone subassemblies are mounted to the rear of the rearview mirror assembly and are spaced apart at opposite ends of the mirror assembly. This arrangement provides several advantages, particularly when the microphone output is provided to a digital signal processor (DSP).
Prior microphone arrays consist of two or more microphones that have nearly identical characteristics and operate in nearly identical conditions. Such arrays can be linear, two-axis, or even three-axis. Typically, linear arrays are used to get maximum benefit cost ratio. A linear array can only achieve directional advantage in the planes containing the axis of the line of centers. A linear array cannot differentiate between these planes so the beam that aims at the driver also aims at a cone of locations around the axis of centers. Only the native transducer directional aspect is available to differentiate. Typically, microphone transducers having cardioid response curves are used to reduce the rear-facing planes. Microphone arrays get their noise reduction advantages by time of arrival alignment for sounds coming from the desired speech location and exploiting the resulting de-correlation of noise sources. The present assumption is that all de-correlation comes from the time stagger and noise enters from a different horizontal angle than desired speech.
Prior art array microphones are based on the use of the same basic directional aspect. This is often a requirement such that when time of arrival is adjusted, the speech signals will add. Differences in aiming angle would interfere with this addition for sounds coming off axis which the array aiming ability requires. In prior art arrays, the microphone transducers must be placed close enough together to achieve time alignment by simple maximization of signal. This prevents wide spacing relative to the wavelength of the highest frequency sound in the pass band. Conversely, a wide enough separation is often required to have a difference of meaningful size when the wavelength decreases. The combination of these two effects typically forces the use of more than two transducers to get effective array microphone operation through the entire audio band.
In a horizontal microphone array, there is a direct tradeoff between reducing noise and harming desired speech coming from passengers in the vehicle. Typical microphone arrays reject speech from passengers as well as noise. Although the prior art microphone arrays are able to reject noise from the opposite side of the vehicle cabin, in doing so, they also reject the speech from passengers on the rejected side. If a conventional horizontal microphone array were positioned either along the top of the rearview mirror assembly or on the bottom of the rearview mirror assembly, all of the microphone transducers would be exposed to the same basic condition such that de-correlation is not present until the time of arrival difference is present. Since the spacing between the microphone transducers must be relatively small, there is a strong likelihood for overlap of noise caused by flowing air effects, particularly flowing air effects originating from the vehicle defroster.
It is highly desirable to provide voice recognition systems in association with vehicle communication systems, and most preferably, such a system would enable hands-free operation. Hands-free operation of a device used in a voice recognition system is a particularly challenging application for microphones, as the accuracy of a voice recognition system is dependent upon the quality of the electrical signal representing the user's speech. Conventional hands-free microphones are not able to provide the consistency and predictability of microphone performance needed for such an application in a controlled environment such as an office, let alone in an uncontrolled and noisy environment such as an automobile.